You wish to cut down an 8-foot sheet of plywood from 96 inches to92-5/8 inches. You position the hook of your steel tape measure onthe left end of the sheet so that the top edge of the tape iseverywhere flush with the top of the sheet's edge. You make a pencilmark at 92-5/8 inches. So far so good.

But what if the steel tape is hooked at the left end correctly but theright end -- the end where you're going to make a pencil mark at92-5/8 inches -- is low by 1 inch? I can see that the resulting cutwill be short, but I can't figure out by how much.

Is there a formula? It seems like there should be, but I never tookwhatever area of math would teach me this.

Idealized, I think of a circle of radius 1 centered on the X and Yaxes. If I measure from the origin STRAIGHT right 1 unit, themeasurement is correct, but if I measure out 1 unit when the ruler iserroneously TILTED DOWN a certain distance, the spot I mark will beshort.

Is there a formula that converts this erroneous distance, whichpresumably describes an angle, to a calculated distance of error? Ialso do understand that the longer is the distance from the origin tothe marked spot, the less the error will be.

Asked perhaps yet another way, as a radius is swept through a circle,how does the X-axis value shrink as it sweeps from a given y-value toa smaller one? I think.